[mlir][Linalg] Add a hoistRedundantVectorTransfers helper function

This revision adds a helper function to hoist vector.transfer_read /
vector.transfer_write pairs out of immediately enclosing scf::ForOp
iteratively, if the following conditions are true:
   1. The 2 ops access the same memref with the same indices.
   2. All operands are invariant under the enclosing scf::ForOp.
   3. No uses of the memref either dominate the transfer_read or are
   dominated by the transfer_write (i.e. no aliasing between the write and
   the read across the loop)

To improve hoisting opportunities, call the `moveLoopInvariantCode` helper
function on the candidate loop above which to hoist. Hoisting the transfers
results in scf::ForOp yielding the value that originally transited through
memory.

This revision additionally exposes `moveLoopInvariantCode` as a helper in
LoopUtils.h and updates SliceAnalysis to support return scf::For values and
allow hoisting across multiple scf::ForOps.

Differential Revision: https://reviews.llvm.org/D81199

1 files changed, 2 insertions, 1 deletions

diff --git a/mlir/lib/Transforms/LoopInvariantCodeMotion.cpp b/mlir/lib/Transforms/LoopInvariantCodeMotion.cpp
index 5fee7d62..0a78cb4 100644
--- a/mlir/lib/Transforms/LoopInvariantCodeMotion.cpp
+++ b/mlir/lib/Transforms/LoopInvariantCodeMotion.cpp
@@ -17,6 +17,7 @@
 #include "mlir/IR/Function.h"
 #include "mlir/Interfaces/LoopLikeInterface.h"
 #include "mlir/Interfaces/SideEffectInterfaces.h"
+#include "mlir/Transforms/LoopUtils.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
@@ -73,7 +74,7 @@ static bool canBeHoisted(Operation *op,
   return true;
 }
 
-static LogicalResult moveLoopInvariantCode(LoopLikeOpInterface looplike) {
+LogicalResult mlir::moveLoopInvariantCode(LoopLikeOpInterface looplike) {
   auto &loopBody = looplike.getLoopBody();
 
   // We use two collections here as we need to preserve the order for insertion